1. Field of the Invention
The present invention is directed to a method for removing or decreasing color from a solution. More particularly, this invention is a process for removing or decreasing the amount of color in a clear, high density brine used in oil or gas wells by adding hydroxylamine or hydrazine.
2. Description of the Prior Art
Clear, high density brines are used in oil well completions and workovers. They are also used as oil well packer fluids. Packer fluids are the fluids which are left in the annular space between the tubing and casing of oil wells. The primary purpose of thee fluids is to balance the pressure in the well so as to prevent a well "blow out" without losing the fluid to the formation, and without damaging the formation as is done when solids-laden fluids are used. The densities required by these brines are determined by the well pressures and depths.
Oil well brines are usually prepared by blending different amounts and types of salt solutions to get the required density and clarity at the lowest cost. Such brines must be clear, that is, free of solids or solids forming materials. Sometimes these brines have color immediately after preparation and the amount of color may increase with time. Alternatively, color can be acquired upon aging or upon blending various brines. Brines are oftentimes blended to obtain a desired density. The cause of the color is not always apparent. Color related problems may have originated in the brine manufacturing process or impurities of some type may be "picked-up" during shipping, storing, handling or during the use of the brine "downhole" in a hot oil well.
The problem of color removal in calcium bromide brines is of particular interest. Calcium bromide brines can be prepared in a number of ways yet, generally, some degree of color is imparted to the brine irrespective of the exact method of preparation. Metal bromides such as calcium bromide can be prepared by contacting a basic alkaline earth metal compound in an aqueous medium with bromine in the presence of a lower alkanol as a reducing agent. Calcium bromide brines can also be prepared using hydrogen bromide and lime.
U.S. Pat. No. 4,083,942 discloses the preparation of alkali and alkaline earth metal bromides by reacting a basic compound of an alkali or alkaline earth metal with a reducing agent in the presence of water followed by the addition of alternate portions of bromine and a basic compound while maintaining the pH at less than 7.0.
More recently, it was disclosed in U.S. Pat. No. 4,248,850 that alkali and alkaline earth metal bromides could be prepared by contacting in an aqueous medium a basic metal compound and bromine in the presence of added formaldehyde as a reducing agent.
In U.S. Pat. No. 3,431,068, there is disclosed a method of preparing alkali metal halides but not alkaline earth metal halides by reacting an alkali metal hydroxide with an elemental halogen in a liquid, saturated aliphatic or alicyclic alcohol or ketone, or a saturated aliphatic aldehyde. According to this process, the formation of unwanted halate salt by-products associated with alkali metal halide production is dimished or eliminated.
It is economically advantageous to treat new or used metal bromide solutions in a manner which eliminates color U.S. Ser. No. 408,035 filed Aug. 13, 1982 now U.S. Pat. No. 4,472,285, claims the use of zinc to remove color causing iron impurities from a brine. However, the source of the color may not be detectable and alternative techniques for color removal in brines are necessary. It is desirable to keep these fluids clear and colorless with minimal cost.